1. Field of the Invention
The present invention relates to a thin film head for use in a magnetic disk apparatus, particularly, to a thin film head for high coercivity media suitable for high density recording, a producing method thereof, and a magnetic disk apparatus.
2. Description of Background
In recent years, as the recording density of magnetic disk apparatuses has been increased, there has been strongly required development of thin film heads excellent in read/write characteristics together with improvement of the performance of recording media. At present, as a reading head, there is used a head using a MR (magnetoresistive effect) element or a GMR (giant magnetoresistive effect) element capable of providing high read output. Further, a TMR (tunnel magnetoresistive) element capable of providing a higher reading efficiency is developed. On the other hand, as a recording head, a prior art inductive thin film recording head using electromagnetic induction is used. A read/write type thin film head integrally forming the reading head and the recording head is employed.
To improve the recording characteristics of a thin film head, a strong and steep recording magnetic field must be generated in order to sufficiently record on recording media having a high coercivity. The track width is reduced with increasing of the track density. Magnetic saturation is caused at the magnetic pole front end portion of the thin film head so as to decrease the recording magnetic field. To cope with increasing of the track density, the processing accuracy of the small track width must be increased.
As shown in FIG. 3, a prior art thin film head has a substrate 1 made of a non-magnetic material. A lower magnetic shield 2 made of a soft magnetic material for enhancing the reading resolution to eliminate the influence of the external magnetic field is provided thereon. A reading gap 3 made of a non-magnetic insulating material is provided thereon. A reading element 4 consisting of an MR or GMR element is disposed in the reading gap. A lower magnetic pole 5 made of a soft magnetic material serving as an upper magnetic shield is provided thereon. A recording gap layer 6 and a coil insulating layer 7 are provided thereon. Lower layer coils 8 and upper layer coils 8′ are disposed in the coil insulating layer. There may be a case of only one coil layer. An upper magnetic pole 9 made of a high saturation magnetic flux density material is provided. The entire head is protected by a protective layer 10. A rear end portion of upper magnetic pole 11 is contacted magnetically with the lower magnetic pole 5 through a through hole of the insulating layer 7 and the recording gap layer 6. The width of a front end portion of upper magnetic pole 12 in a floating surface 13 is processed into a width corresponding to the track width. The coils 8 and 8′ are constructed so as to be arranged circumferentially about the rear end portion of upper magnetic pole.
A recording electric current is applied to the coils 8 and 8′ so as to induce a magnetic flux in the upper magnetic pole 9 and the lower magnetic pole 5. A recording magnetic field generated from the front end of the recording gap records a signal onto a recording medium 14 moving slightly away from the floating surface 13. The magnetic flux is concentrated in the vicinity of the recording gap from the lower magnetic pole and the upper magnetic pole. As a result, a high magnetic field is generated. The length in the front end portion of upper magnetic pole is contacted with the recording gap layer 6 is called a gap depth Gd. As the length is reduced, the recording magnetic field is increased since the magnetic flux is concentrated onto the magnetic pole front end.
When the upper magnetic pole 9 is formed, a photoresist is coated onto the coil insulating layer 7 and the recording gap layer 6. The photoresist is exposed and developed through a predetermined mask of the shape of the upper magnetic pole so as to remove the photoresist in a portion to be the shape of the upper magnetic pole. A high saturation magnetic flux density material as the upper magnetic pole is formed in the removed portion by a plating method. In the prior art thin film head, as described above, the photoresist for forming the upper magnetic pole is formed on a high and steep slope 15 of the coil insulating layer 7. When the photoresist is exposed, the shape of the upper magnetic pole cannot be formed accurately due to light reflection from the slope and insufficient depth of focus. In particular, a problem arises when a small track width of the rear end portion of upper magnetic pole is formed.
As a method for solving this point, as described in Japanese Published Unexamined Patent Application No. 2000-276707, there is proposed a method for separating an upper magnetic pole into an upper magnetic pole front end layer, an upper magnetic pole rear end layer, and an upper magnetic pole top layer. In this method, as shown in FIG. 4, a recording gap layer 6 is formed, and then, a first non-magnetic insulating layer 16 for defining a gap depth. A photoresist for forming an upper magnetic pole front end layer 17 and an upper magnetic pole rear end layer 18 is formed thereon. The photoresist is exposed and developed to remove portions to be the shapes of the upper magnetic pole front end layer 17 and the upper magnetic pole rear end layer 18. A high saturation magnetic flux density material as the upper magnetic pole front end layer 17 and the upper magnetic pole rear end layer 18 is formed in the removed portions by a plating method. Further, the gap between the upper magnetic pole front end layer 17 and the upper magnetic pole rear end layer 18 is buried by a second non-magnetic insulating layer 19. The upper magnetic pole front end layer 17, the upper magnetic pole rear end layer 18, and the second non-magnetic insulating layer 19 are flattened by polishing. A coil insulating layer 7, lower layer coils 8, upper layer coils 8′, an upper magnetic pole top layer 20, and a protective layer 10 are formed thereon. In this method, the photoresist for forming the upper magnetic pole front end layer 17 is formed on the first non-magnetic insulating layer 16 having a step smaller than that of the slope 15 of the coil insulating layer in the prior art shown in FIG. 3. The problems of light reflection from the substrate or insufficient depth of focus can be eliminated so as to enhance the small track width processing accuracy.
In the thin film head shown in FIG. 4, the upper magnetic pole front end layer 17 is formed on the step of the first non-magnetic insulating layer 16. A very small track width of 0.4 μm or less which has been required in recent years is difficult to be formed at high accuracy.
As the track is smaller and the coercivity of the media is higher, the recording magnetic field required for the recording head is increased more and more.